INNER ROTOR KIT FOR XR50/CRF50 This product is a built-in magnetic rotor structure. It can get rid of the weight of flying wheel magnetic rotor so the engine becomes light and speedy. The engine can run freely and well from idling to high speed of 1,5000 RPM. This product can be used for various engines of racing bikes. It works better in all stock or high performance motors because the motor can rev free with not as much weight on the crankshaft. Eliminate the weight of your flywheel and let your motor really twist like a 2-stroke.  Kit allows you to set and build in timing into your motor. This unit is good up to 15,000 RPM's.. A must for that full race motor. Fits - XR50, CRF50, XR70, Pitbike and Mini ATV Engines: XR/CRF 50, 70, Z 50, 70CC, 110CC, 125CC & 138CC BBR, Thumpstar, SSR, Sikk MX. most Chinese made and most HONDA Horizontal kick start engines, will not work on electric start engines.